As a fuel supply system for supplying hydrogen gas used as a fuel gas to a fuel cell, there have been known a type using a high-pressure hydrogen tank filled with high-pressure hydrogen gas or a hydrogen storing tank filled with a hydrogen storing alloy which allows hydrogen gas to be reversibly stored and discharged. For instance, the publication of Japanese Patent Application Laid-Open No. 2005-226715 discloses a fuel supply system which has a plurality of hydrogen tanks connected in parallel to a fuel cell through the intermediary of a hydrogen pipe, an on-off valve being installed to each of the hydrogen tanks. The fuel supply system is adapted to open all the on-off valves at the same time when the fuel cell system is in operation.